Why Stress Might Make You Sick

MONDAY, April 2 -- A new study involving the common cold may help explain why stress, which dampens the immune system, seems to trigger inflammation in many people.

That would appear contradictory, because the immune system creates inflammation (for example, the redness around a wound) to help the body heal. But the research suggests that high and long-term levels of stress contribute to inflammation.

In turn, the inflammation can lead to conditions such as heart disease, asthma and autoimmune disorders, in which the immune system turns against the body.

The research "suggests the kind of diseases that are going to be affected by stress," said study lead author Sheldon Cohen, professor of psychology at Carnegie Mellon University in Pittsburgh. "They're diseases in which inflammation is a key aspect."

Over the past five to six decades, researchers have linked stress to disease, Cohen said. "There's not much question that stressed people are at greater risk for developing some of these diseases or having them become more severe. A little bit less clear is exactly how that happens. How does stress get under the skin to affect disease outcomes?"

One possibility is that stressed people are simply unhealthier -- smoking and drinking more and sleeping less. In that area, the challenge is figuring out which came first, stress or unhealthy decisions.

The other possibility is that the body's hormones that respond to stress play a role.

In the new study, investigators performed two experiments, involving more than 300 people, to gain more insight. The researchers asked the participants about the stresses in their lives and then exposed them to cold viruses to see if they got sick.

After adjusting the statistics for various factors, the researchers found that people whose bodies had higher levels of ongoing psychological stress -- such as that caused by divorce -- were less able to dampen inflammation. This seemed to have something to do with their immune cells being less sensitive to a hormone that turns off inflammation.

The people with more stress were also at higher risk of developing a cold, according to the report published online April 2 in the Proceedings of the National Academy of Sciences.

Dr. Andrew Miller, a professor of psychiatry and behavioral sciences at Emory University School of Medicine who studies how stress affects the immune system, said the research "provides a very concrete example of how chronic stress and its effects on the immune system can affect our daily lives in a very real-world context."

However, this is just part of a wider picture of how stress affects the body, Miller cautioned.

"In ancestral times, a stressful environment would have a high likelihood of involving some form of fighting and being wounded and thereby infected," he said. "Inflammation is a process in the body that is essential to fighting infections and healing wounds. Therefore, the induction of inflammation by stress is a way for the body to prepare itself for battle in an environment that represents danger of attack."

While the study uncovered an association between chronic psychological stress and inflammation, it did not prove a cause-and-effect relationship.